Low-noise static-discharge apparatus



April 19, 1960 R. L. TANNER LOW-NOISE STATIC-DISCHARGE APPARATUS Filed March 15, 1957 INVENTOR. 205E274. ZW/V/VEQ LOW-NOISE STATIC-DISCHARGE APPARATUS Robert L. Tanner, Menlo Park, Calif.

Application March 15, 1957, Serial No. 646,465 12 Claims. (Cl. 343-899) This invention relates to static-discharge systems and, more particularly, to an improvement in such systems wherein radio interference arriving from static discharge is minimized.

may serve to reduce the corona discharge noise some what, but it is still present. Also, attempts have been made without much success to findl antistatic coatings. Presently favored are wick dischargergbut there is still considerable noise present.

An object of the present invention is to decouple the noise arising due to corona discharge.

Another object of. the presentinvention is to provide a novel, static-discharge noise-decoupling arrangement,

'Still, another object of the, present invention is to provide a static-discharge arrangement which can reduce the noise caused as a result of such discharge to a minimal value.

These and other objects of the invention are achieved in an arrangement whereby advantage is taken of the fact that anantenna is a reciprocal transducer. From this, it can be shown that when an antenna is excited with a radio-frequency voltage, the radio-frequency electric fieldstrength existing at any point of space in the result ing field pattern is an indication of the strength of the signal which the antenna will receive from a noise source located at that point within the electric field. Thus, at points where no field is produced by an antennarexciting voltage, no signal will be received by the antenna from signal soiuces placed at these points. Thus, to minimize noise due to discharges, the discharges should be induced to occur from points at which no fieldwill be produced by a voltage at the antenna terminals. In accordance with this invention, means are provided for inducing discharges at null points within the field pattern of an. antenna. This minimizes the noise due to corona or static discharges.

The novel features that. are considered characteristic of this invention are set. forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in conneetion with the accompanying drawings, in: which:

Figure 4 is a view in section of the embodiment of the invention shown in Figure 3; and

. to the antenna terminals.

that the radio field tends to concentrate at extremities Figure 1 shows an isometric view of anembodiment of the invention;

Figure 2 shows in'section the embodiment of the invention in an RF field configuration toassist in an understanding of this invention;

Figure 3 is. another isometric view of another embodiment of this invention; 7

Figure 5 is a view illustrating the relative positions of a receiver, an antenna, and static decouplers in conjunc-' tion with an aircraft.

The description that follows will be directed to the application of the invention to aircraft, since corona discharge is most troublesome with aircraft. However, this is not to be construed as a limitation upon the invention, since it will be readily recognized by those skilled in the art that the principles explained and exemplified herein are applicable to receivers in any location where they pick up undesirable noises from corona discharges. 7 A radio-frequency voltage applied to antennaterminals on an aircraft produces an electric field in space. In general, it can be said that such field tends to concentrade at the extremities of the aircraft and will" be; par? ticularly concentrated at sharp points and edges at i the' extremities. 'Inthis respect, radio-frequency fields are terminal current can be said to be a measure of the radio noise produced by the discharge.

A corona-discharge current is very localized in space, occupying only a very small volume. Considered "as a function of time, such currents flow as very sharp pulses. Each of these sharp pulses has significant components at relatively high radio frequencies. It is known that an antenna is a reciprocal device. From this, it can be shown that the noise signal which arises. in the antenna from a corona pulse is proportional to the strength of the electric field created at the point where thecorona discharge takes place as the result of applying a voltage It was'previously pointed out in sharp. points in a manner similar to the direct-current field producing the discharge. In other words, the 'diSw charges tend to occur at just those points where coupling 7 to the antenna is maximum. Under normal circumstances, if the configuration of the radio-frequency field which measures the coupling, is examined, it will be found that if only a small region is considered (about awingtip, for example), the shape of. the radio-frequency field is the same as the direct-current field that would exist at the point if the entire aircraft. were raised to a high potential. Where the direct-current fields are high, leading to discharges, the radio-frequency fields are also high, leading to high coupling. Therefore, in order to effect decoupling, iris necessary to. exploit the basic diiterences between the radio-frequency anddi rect-current fields in such a way as to allow high direct. current or static fields to occur at points Where the radia frequency field is small. This. decoupling. isiac cornplished by this invention. h i i i 1" i Referring now to Figure. 1, there is shown one embodiment of the invention. The wingtip 110 of an airplane has attached thereto a rope 12, which may either be fabricated of a material having: a. high resistance or-be an insulating material coated with a. high-resistance coating. The rope is attached to what may be termed a tubular electrode 14. This includes a crossesupporting conductive member 16, to which 'the 'rope. is attached, and which itself is attached to the cylinder 1 8. Around the equator of the cylinder are a plurality of discharge elements or points 29, which are made from tungsten at the end of the distributed resistance 12, appears isolated to the radio-frequency field while appearing to the static field as a projection from the wing.

This may better be seen in Figure 2, wherein the embodiment of the invention is shown in section. If a radiofrequency voltage is applied to the antenna terminals, creating a radio-frequency field in the vicinity of the wingtip, the impedance of the resistance rope 12 would be extremely high relative to the reactance of the space be tween the wingtip and the electrode, so that the electrode appears isolated as far as the radio frequency field is concerned. The radio-frequency field configuration 22 has the appearance represented by the'dashed lines, which may be termed the field lines. As indicated by the figure, it will be seen that there are as many lines leavingthe isolated body or electrode 14 as enter it. This means that at some point on the body lines neither enter nor leave, which signifies that atthis point the RF coupling field is zero. Therefore, discharges occurring from these points situated at the null point of the radio field do not coupleappreciably to the receiver antenna. Further, it is well known to those acquainted with the art that at the tips 20' a concentration of the direct-current field will I occurso that these points go into corona easily.

j In Figures 1 and 2, the conducting cylinder is shown at the end of a resistive rope. The conducting cylinder may be replaced by a sphere, or, indeed, may be any shape, provided that the conducting body is isolated with respect to the radio-frequency field of the. antenna of concern. The lengthof the rope is'immaterial, provided it has alsuificient distributed resistance to provide the required radio-frequencyfield isolation. "I t is evident that the principles described above are equally applicable to both a two-dimensional field geometry, as well as to a three-dimensional field geometry. Thus, if preferred, a flush-mounted permanent-discharger installation may be. employed. Figures 3 and 4 show such an embodiment of the invention. The metal at the surfaces near and extending to the tips of the wings and other surfaces may be replaced by some form of plastic structure 30, such as a combination of structural Fiberglas and resin with a metal cylinder embedded in the tips, or preferably some form of a metal overlay 32. The plastic structure may be rendered slightly conductive by the addition of a 'lampblack to the resin before layup, or by coating with a resistive paint. The wingtip metal overlay has attached theretoa plurality of sharp metal discharge points 34. The location of these discharge points is along the line where the radio-frequency field is zero. The trailing edge 36 of the metal overlay i s'given a sufficiently large radius to insure that there is no tendency for discharges to'occur there, these discharges should only occur at the points. The extent of the plastic structure must be, as in the case of the resistive rope, sufficient to provide the required radio-field isolation for the metal overlay. The location for the discharge may either be calculated or measured using electrolytic tank techniques.

The embodiments of the invention described, in addition to producing very low noise, also have the advantage that they can be built to have almost any desired discharge capacity. The current from any discharger is limited by space charge. Current leaving the discharger is carried away as ions. These move with finite speed, which in an aircraft in flight is essentially the slip- 'stream velocity. There is, however, a components of motion 'dueto the electric field. The fact that the ions move at finite speed means that there is alwaysa cloud of ions surrounding the discharge point, and these ions have the same sign as the charge which is attempting to escape. The effect of this charge cloud is to diminish the field at the point, thereby limiting the amount of charge leaving the point. In the flush-mounted discharger, shown in Figures 3 and 4, the row of points acts like a line source of ions, rather than a point source. The space W q M.-

.4 charge is more widely distributed in space, so that its shielding eifect is less. In addition to this basic advantage, the discharger section can be made as long as necessary without compromising the aerodynamic characteristics of the aircraft. In this way, dischargers of capacity adequate to discharge even large, high-speed aircraft can be built. Figure 5 illustrates the relative locations of a receiver, an antenna, and static dischargers, in accordance with this invention, on the body of an airplane 38. Three receivers 40, 42, 44 (represented by rectangles) are shown, positioned at the forward end of the airplane 38. One of these 40 is used in conjunction with a flush-mounted automatic direction finder 46, which has its sense antenna (not shown) recessed in the belly of the aircraft. The second and third of the receivers 42, 44 are connected to their antennas (respectively represented by rectangles 48, 50) which are usually located under a plastic cover on the tip of the vertical stabilizers 52 of the airplane. The antenna 48 represents one which is employed as the Loran antenna, and the antenna 50 may be employed as the high-frequency receiving antenna. The locations of the embodiments of the invention are represented by the groups of lines 54, 56, 58, 60, 62, which extend respectively from the outer tips of the wings, the outer tips of the horizontal stabilizers, and the top of the vertical stabilizer.

Accordingly, there has been shown and described above a novel, useful, unique, and simple arrangement for minimizing the noise arising as a result of corona or static discharges in an antenna by establishing the apparatus for discharging corona at null points within the radiof'requency field of the antenna yet preserving the con-v nection of the apparatus with the surfaces to be protected against corona discharges. Although the embodiments of the invention have been described in connection with an aircraft, it will be understoodthat the invention may also take other forms and can be used to minimize corona noise caused at stationary structures or on other vehicles or devices. These other uses and forms are also intended to be included within the spirit of this invention and the scope of the claims appended herein.

I claim:

1. In a system of the type wherein noise from corona discharges are detected at the terminals of an antenna, an improved noise minimizing arrangement comprising means for discharging corona, and means for supporting said means for discharging corona. at a null point within the radio-frequency field of the antenna.

2. In a system of the type wherein noise from corona discharges caused by a direct-current field are detected at the terminals of an antenna, an improved noise minimizi'ng arrangement comprising a corona discharge element, and means for supporting said corona discharge elementat a null point within the radio-frequency field of said antenna yet still within the direct-current field.

3. In a system as recited in claim 2 wherein said means for supporting said corona discharge element at a null point includes a conductive body and a resistive element connected to said body.

4. A static-discharge noise-decoupling device for a structure including a receiver having an antenna, said structure having surface tips at which corona discharges occur comprising a body having a conductive surface, a plurality of discharge points mounted at radio-frequency field null points on the surface of said body and distributed resistance means for holding said body spaced from said surface tips.

5. A static discharge noise-decoupling device for a structure having surface tips at which corona discharges occur as recited in claim 4 wherein said body is a metal cylinder, and said means for holding said body is a resistive rope having one end attached to said surface tips and the other end to said metal cylinder.

I 6. A static-discharge noise-decoupling device v for a structure as recited in claim 4 wherein said distributed rality of corona discharge elements positioned along said metal overlay said plastic sheets extending from said vehicle surface a suificient distance to place said corona discharge elements in the null region of the radio field of said antenna.

8. A static-discharge noise-decoupling device for an aircraft carrying a receiver antenna and having vvingtip surfaces at which corona discharges occur comprising a metal body having a circular surface, a plurality of corona discharge points mounted symmetrically over said circular surface, and a resistive rope having one end attached to said tip surfaces and the other end to said metal body, the length of said rope being sufficient to maintain said metal body at the null point within the radio-frequency field of said receiver antenna. a

9. In an aircraft carrying a receiver antenna and having wingtips subject to corona discharges, an improved static discharge noise-decoupling arrangement comprising distributed resistance means at said wingtips including plastic sheets extending from said wingtips toward the wing surfaces, means rendering said plastic sheets resistive, a conductive metal termination for said wingtips, and a plurality of corona discharge points supported from said conductive metal termination along a null region of the radio-frequency field of said antenna.

10. In an aircraft carrying a receiver antenna as recited in claim 9 wherein said conductive metal termination for said wingtips includes a metal overlay over said plastic sheets.

11. The method of decoupling noise from a receiver having an antenna which picks up said noise from corona discharges caused by a direct-current field comprising establishing a null region of said antenna radio field Within said direct-current field, and establishing said corona discharge at said null region.

12. In a vehicle carrying a receiver having an antenna which picks up noise from corona discharge points the method of decoupling said noise comprising establishing a null region of said antenna radio field, and resistively supporting said corona discharge points within said null region from said vehicle.

References Cited in the file of this patent UNITED STATES PATENTS 1,893,287 Jenkins Jan. 3, 1933 2,243,618 Brown May 27, 1941 2,309,584 George Jan. 26, 1943 2,397,118 Bennett Mar. 26, 1946 FOREIGN PATENTS 690,379 Great Britain Apr. 22, 1953 

